A traditional injection device comprises a piston device including an inner chamber wherein the liquid is pressurized, and an injection head, or injection nozzle, fluidicly connected to the piston device. A connection duct communicates the pressurized liquid from an outlet port of the inner chamber toward the injection head. When the injection device is part of a hydroforming station, the injection device is designed to inject the liquid at a predetermined pressure profile and flow rate adapted to urge a preform against the wall of a mold cavity having the shape of the container to be produced. Advantageously, the injected liquid is the end product to be contained in the formed container.
Prior to container or bottle production, both the piston device and the injection head have to be purged of air with the liquid, with a minimized liquid loss. Later in this patent application, this operation phase is called “air purge”.
Another operation phase of a piston device connected to an injection head is to allow the liquid in the inner chamber of the piston device to be drained out of the inner chamber through a drainage port. A well-known location of the drainage port is at a lowest point of the inner chamber.
For the production mode, the piston device is arranged to draw in liquid from the liquid source and to inject it at a predetermined pressure and flow rate in the injection head. Maximum pressure in the inner chamber is high, for example as high as 60 bars, but preferably below 40 bars. Piston speed can be as high as 1 m/s generating a flow up to 200 l/s, in particular when the hydroforming station uses forming liquid at a temperature below the glass transition temperature of the preform material. Also, in order to achieve a high production rate of the hydroforming station, the piston head is moved back and forth at high frequency, such as 1 Hz.
The inventors have discovered a problem happening in the piston device of a hydroforming station. As such a piston device has to be operated with simultaneously high liquid pressure and high flow rate, the piston and its sealing gasket may be subjected to mechanical efforts that urge it laterally toward the piston body, with a risk, particularly after some time, of damaging the sealing gasket and experiencing localized and early wear issues, increasing the frequency and cost of maintenance of the system. When the gasket is worn, liquid tightness between the piston head and the piston body is no longer ensured and the piston device is no longer able to fulfil its function of pressurizing the liquid and of urging the liquid toward the injection head. Furthermore, using the piston device in such a state would lead to soiling the hydroforming station with the liquid leaking out of the piston device.
One of the aims of the invention is to provide an injection device that reduces the above mentioned risk of wear.
In case of product changeover, pushing with the new product must not generate product losses or must minimize product losses as much as possible.
Hygiene is a very important criteria in all transition and all production steps to guaranty consumer safety from direct food contact point of view in case of beverage or skin contact for non-food products. For that purpose, prior any production, a cleaning in place (CIP) cycle is conducted. Such CIP is also done at regular intervals during the production phases. The CIP cycle may vary according to the type of product that is produced and according to the producer specification. It is important that during this cycle, a turbulent flow can be created in order to remove any residual contaminant or micro-organism for any area of the injection device in contact with the forming product. A specific care is to be taken on seals and gaskets in order to make sure that cleaning product flow reaches all the recesses and parts in contact with the product.
Another aim of the invention is to provide an injection device that minimizes the CIP time providing a very efficient cleaning, with a minimized amount of cleaning product.